Conventionally, hybrid vehicles, electric vehicles and the like have been known that run by driving force from an electric motor. These vehicles have a battery mounted thereon for storing electric power to be supplied to the electric motor serving as a driving source. The battery is discharged or charged, for example, in consideration of a state of charge of the battery. The state of charge of the battery is calculated based on a value of a current discharged from the battery, a value of a current charged into the battery, a voltage of the battery, and the like. That is, the state of charge is calculated with an estimated value, which may result in a difference between the calculated state of charge and the actual state of charge. In order to increase accuracy of a state of charge, therefore, techniques of initializing a state of charge of a battery have been proposed.
Japanese Patent Laying-Open No. 2002-25631 discloses a battery pack including a secondary battery, a detection unit for detecting a charge/discharge current and/or a charge/discharge voltage of this secondary battery, a state-of-charge calculation unit for calculating a state of charge of the secondary battery based on the detected charge/discharge current value and charge/discharge voltage value, and a display unit for displaying a value of the calculated state of charge. This battery pack further includes a state-of-charge display button for causing, when pressed, a display unit to display the state of charge of the secondary battery. When the state-of-charge display button is pressed to satisfy a prescribed condition, the state-of-charge calculation unit is initialized.
According to the battery pack described in this publication, a switch mechanism for achieving the function of displaying the state of charge of the secondary battery by displaying the state of charge and the function of initializing the state-of-charge calculation unit can be integrated into a single button, thus eliminating the need for separately providing buttons each including a switch mechanism for achieving each function. Accordingly, the number of components can be reduced, thereby minimizing costs. Further, the sharing of the button also reduces a required footprint by half as compared to an example where buttons are separately provided on a case. As a result, a degree of freedom in designing a shape of the battery back is significantly increased.
In the battery pack described in Japanese Patent Laying-Open No. 2002-25631, however, the state of charge cannot be reset unless a user presses the button. Therefore, the state of charge may remain unreset for a long time, which may deteriorate accuracy of the state of charge in a system where a power storage mechanism may repeatedly be discharged and charged frequently, for example.